The present invention relates generally to hydraulic jarring tools.
Bidirectional hydraulic jars have provided much needed versatility in the removal of objects lodged in the casings of oil and gas wells. However, there remains a need for a bidirectional jar that is easily adjustable. There is a need for a jarring tool in which the impact surfaces are enclosed and protected from accumulation of debris and the resulting dampening of the blows. There is a need for a tool in which the exposed shoulders on the tool are champfered to facilitate removal from the well. Still further there is a need for a bidirectional jarring tool that can be re-cocked easily, without firing in the reverse direction, for unidirectional jarring operations. The preferred embodiment of the present invention provides these and other advantages as will be apparent from the following description.
The present invention comprises a bidirectional hydraulic jar. The jar comprises an outer assembly and an inner assembly. The outer assembly comprises a tubular body with first and second ends. The tubular body defines an inner wall, and the first end comprises a connecting portion. A first impact surface is provided on the tubular body to transmit force in a first direction, and a second impact surface is provided on the tubular body longitudinally spaced from the first impact surface to transmit force in a second direction opposite the first direction.
The inner assembly comprises an elongate body having a portion telescopically receivable within the outer assembly. The elongate body defines an outer wall and has first and second ends. The second end comprises a connecting portion. A first impact surface is provided on the elongate body and is adapted to engage the first impact surface on the tubular body of the outer assembly. A second impact surface is provided on the elongate body longitudinally spaced a distance from the second impact surface on the elongate body and adapted to engage the second impact surface on the tubular body of the outer assembly.
An annular elongate fluid chamber is formed between the outer wall of the elongate body of the inner assembly and the inner wall of the tubular body of the outer assembly. The fluid chamber comprises first and second portions and a restrictor portion therebetween. The restrictor portion has a smaller radial dimension than the first and second portions.
A valve assembly is supported in the fluid chamber and fixed to one of the outer wall of the elongate body of the inner assembly and the inner wall of the tubular body of the outer assembly. The valve assembly is sized for reciprocal movement in the restrictor, and is adapted to obstruct fluid flow through the restrictor portion except for a bleed passage therethrough. This arrangement creates a delay as the valve assembly moves through the restrictor portion and accelerated movement as the valve assembly exits the restrictor portion into the first and second portions of the fluid chamber.
The valve assembly comprises a first valve ring comprising first and second ends with a body therebetween. The first end defines a metering face. A second valve ring comprises first and second ends with a body therebetween. The first end defines a metering face adjacent the metering face of the first ring and forms therewith a metering space between the first and second valve rings. The metering space forms part of the bleed passage.
At least one of the first and second valve rings is sized for sealing engagement with the restrictor passage and comprises a pass-though opening continuous with the metering space and forming part of the bleed passage. The size of the metering space is adjustable by moving at least one of the first and second valve rings relative to the other to vary the size of the bleed passage.
In this way, movement of a selected one of the outer assembly and inner assembly relative to the other one in a first direction causes jarring impacts between the first impact surfaces of the outer and inner assemblies to thrust the jar in a first direction. Movement of the selected one of the outer assembly and inner assembly relative to the other one in a second direction causes jarring impacts between the second impact surfaces of the outer and inner assemblies to thrust the jar in a second direction. Adjusting the size of the metering space between the first and second valve rings varies the force and speed of the jarring impacts.